Search

This paper describes a study in which thermomechanical properties of wrought magnesium were thoroughly investigated. The formability of the magnesium based alloy sheet at the elevated temperatures was assessed with a forming testing machine accompanied by a tailor-made temperature control system. The deformed laser printed circles on the magnesium sheet were measured to plot a forming limiting curve. The most used theoretical forming limiting diagram models were adopted to predict the forming limiting curve and the suitability of the model was checked for the formability prediction of the hexagonal close-packed metals at the elevated temperatures. [DOI: 10.1115/1.2977823] Keywords: formability analysis, magnesium alloy, thermomechanical property

This paper is concerned with the study of, both local and global, uniform asymptotic stability for general nonlinear and time-varying switched systems. Two concepts of Lyapunov functions are introduced and used to establish uniform Lyapunov stability and uniform global stability. With the help of output functions, an almost bounded output energy condition and an output persistent excitation condition are then proposed and employed to guarantee uniform local and global asymptotic stability. Based on this result, a generalized version of Krasovskii-LaSalle theorem in time-varying switched systems is proposed. For switched systems with persistent dwell-time, the output persistent excitation condition is guaranteed to hold under a zero-state observability condition. It is shown that several existing results in past literature can be covered as special cases using the proposed criteria. Interestingly, as opposed to previous work, the main results of this paper are applicable to the situation where some switching systems are not asymptotically stable at the origin. The robust practical regulation problem of nonholonomic mobile robots is studied as a way of demonstrating the power of the proposed new criteria. A novel switching controller is proposed with guaranteed robustness to orientation error and unknown parameters in mobile robots. Index Terms--Lyapunov functions, mobile robots, nonlinear time-varying systems, persistent excitation, robust regulation, switched systems, uniform asymptotic stability, zero-state observability.

This paper presents new characterizations of uniform global asymptotic stability for nonlinear and time-varying discrete-time systems. Under mild assumptions, it is shown that weak zero-state detectability is equivalent to uniform global asymptotic stability for globally uniformly stable systems. By employing the notion of reduced limiting systems, another characterization of uniform global asymptotic stability is proposed on the basis of the detectability for the reduced limiting systems associated with the original system. As a by-product, we derive a generalized, discrete-time version of the well-known Krasovskii-LaSalle theorem for general time-varying, not necessarily periodic, systems. Furthermore, we apply the obtained stability results to analyze uniform asymptotic stability of cascaded time-varying systems, and show that some technical assumptions in recent papers can be relaxed. Through a practical application, it is shown that our results play a similar role to the classic LaSalle invariance principle in guaranteeing attractivity, noting that reduced limiting systems are used instead of the original system. To validate the conceptual characterizations, we study the problem of sampled-data stabilization for the benchmark example of nonholonomic mobile robots via the exact discrete-time model rather than approximate models. This case study also reveals that in general, sampled-data systems may become non-periodic even though their original continuous-time system is periodic. A novel sampled-data stabilizer design is proposed using the new stability results and is supported via simulation results. Index Terms--Cascaded systems, discrete-time systems, mobile robots, reduced limiting systems, sampled-data controllers, uniform global asymptotic stability, weak zero-state detectability.

This paper presents a formability analysis of tailor-welded blanks (TWBs) made of cold rolled steel sheets with varying thicknesses. Steel sheets ranging between 0.5 mm, 0.6 mm, 0.7 mm, 0.8 ram, 0.9 mm, and 1.0 mm in thickness were used to produce TWBs of different thickness combinations. The primary, objective of this paper is to characterize the effects of thickness ratios on the forming limit diagram (FLD) for a particular type of TWB. The TWBs chosen for the investigation are designed with the weld line located in the center of the specimens perpendicular to the principal strain direction. Nd: YAG laser butt-welding was used to prepare different tailor-made blank specimens for uniaxial tensile tests and Swift tests. The experimental results of the uniaxial tensile test clearly revealed that there were no significant differences between the tensile strengths of TWBs and those of the base metals. After the Swift tests, the formability of TWBs was analyzed in terms of two measures: The forming limit diagram and minimum major strain. The experimental findings indicated that the higher the thickness ratio, the lower the level of the forming limit curve (FLC) and the lower the formability of the TWBs. The findings also show an inverse proportional relationship between thickness ratios and minimum major strains. TWBs with a thickness ratio of close to 1 were found to have a minimum major strain closer to those of base metals. The effects of different thickness ratios on TWBs were further analyzed with a finite element code in a computer-aided engineering package, PAM-STAMP, while the failure criteria of the TWBs in the finite element analysis were addressed by the FLCs which were obtained from the experiments. However, the weld of the TWB in the simulation was simply treated as a thickness step, whereas its heat affected zones were sometimes disregarded, so that the effects of the thickness ratio could be significantly disclosed without the presence of weld zones. The results of the simulation should certainly assist to clarify and explain the effects of different thickness ratios on TWBs. [DOI: 10.1115/1.2034518] Keywords: formability analysis, tailor-welded blanks, thickness ratio

5-Enol-pyruvylshikimate-3-phosphate synthase from Agrobacterium sp. CP4 (CP4 EPSPS) confers tolerance to the nonselective herbicide glyphosate (marketed under the trade name Roundup (1)) when sufficiently expressed in transgenic plants. Dual CP4 EPSPS transgene cassettes were transformed into corn (Zea mays L.) under the transcriptional regulatory control of the rice (Oryza sativa L.) actin 1 (P-Ract1) and the enhanced Cauliflower mosaic virus 35S (P-e35S) promoters, respectively, to impart fully constitutive expression in corn. Resulting events were tested for lack of chlorosis and malformation injury after two sequential applications of 1.68 kg acid equivalents (a.e.) [h.sup.-1] glyphosate. Agronomic parameters, male fertility, appropriate Mendelian segregation of the trait, plus characteristics of the transgenic integration site were also evaluated. From this selection process, the NK603 event was chosen for commercialization as the event that embodied the most optimal profile of tolerance, agronomics, and molecular characteristics. The NK603 event exhibited high glyphosate tolerance from one transgenic locus bearing a single copy of the dual cassettes integrated into the corn genome with a minimum of target sequence disruption. Trait expression in the NK603 event has remained stable over more than eight generations as shown through tolerance testing, western blots of CP4 EPSPS accumulation, and Southern blot analysis of the transgene., AGRICULTURAL CROPS tolerant to the herbicide glyphosate (N-phosphonomethyl-glycine) have been planted on increasing numbers of hectares since the introduction of the glyphosate-tolerant 40-3-2 soybean event in 1996 (Padgette et al., [...]